4 MARK SCHEME AS Chemistry Specimen paper 02.3 Ions, not molecules, will interact with and be accelerated by an electric field Only ions will create a current when hitting the detector AO2e AO2e 4 of 3

8 MARK SCHEME AS Chemistry Specimen paper 05.2 This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question. Level marks Level marks All stages are covered and the explanation of each stage is generally correct and virtually complete. Stages and 2 are supported by correct equations. Answer communicates the whole process coherently and shows a logical progression from stage to stage 2 and then stage 3. The steps in stage 3 are in a logical order. All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete. Answer is mainly coherent and shows a progression through the stages. Some steps in each stage may be out of order and incomplete. 6 2 AOa 4 AO3 2b Indicative chemistry content Stage : formation of precipitates Add silver nitrate to form precipitates of AgCl and AgBr AgNO 3 + NaCl AgCl + NaNO 3 AgNO 3 + NaBr AgBr + NaNO 3 Stage 2: selective dissolving of AgCl Add excess of dilute ammonia to the mixture of precipitates the silver chloride precipitate dissolves AgCl + 2NH 3 Ag(NH 3 ) Cl Stage 3: separation and purification of AgBr Filter off the remaining silver bromide precipitate Wash to remove soluble compounds Dry to remove water Level 2 marks Level 0 0 marks Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete. Answer includes some isolated statements, but these are not presented in a logical order or show confused reasoning. Insufficient correct chemistry to warrant a mark. 8 of 3

10 MARK SCHEME AS Chemistry Specimen paper 06. Extended response Stage : appreciation that the acid must be in excess and calculation of amount of solid that permits this. Statement that there must be an excess of acid AO2d Maximum of 7 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured. Moles of acid = /000 = mol 2 mol of acid react with mol of calcium hydroxide therefore moles of solid weighed out must be less than half the moles of acid = = mol AO3 2a AO3 2b Mass of solid must be < = < 0.37 g Stage 2: Experimental method. AO3 2a Measure out 50 cm 3 of acid using a pipette and add the weighed amount of solid in a conical flask AO3 2b Titrate against 0.00 (or 0.200) mol dm 3 NaOH added from a burette and record the volume (v) when an added indicator changes colour AO3 2b Stage 3: How to calculate M r from the experimental data. Moles of calcium hydroxide = (v/2 conc NaOH)/000 = z mol M r = mass of solid / z AO3 2a AO3 2a 0 of 3

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